: The tiny square spot to the north-east (point A on the map) is truly inexplicable: I have no clue how it got there, or what it's purpose is.

As you might guess from the map, the tiny, partially-textured room does hold a switch on the north wall. The switch opens the door to the prison cell. The open doorway is untextured, and while you can exit the cell through the door, you can't cross back over the threshold (and back to the exit polygons) once outside. BoB, wait, take me with you! ... Damn, stuck in another hole.